Shield for electrical currents



Nov. 7, 1944. w. F. STAHL SHIELD FOR ELECTRICAL CURRENTS Filed June 25,1941 f I Z fER/YOW METAL 6 PAPER LAM/NATIONS Patented Nov. 7, 1944UNITED STATES PATENT OFFICE snmm) FOR ELECTRICAL CURRENTS William F.Stahl, Evanston, 111.

Application June 25, 1941, Serial No. 399,643 I (01. 174-35) 5 Claims.

This invention relates to shields for electrical currents and moreparticularly to laminated tubular shields wherein a layer or layers ofconducting material is adapted to intercept and dissipateelectro-magnetic and electro-static fields of force set up by highfrequency currents.

In the radio field and in other arts wherein high frequency currents areused, it is often desirable to provide an electrically conducting shieldwhich may be placed around the source of electrical current and willdissipate the electromagnetic and electro-static fields of force set upabout the current source. Thus in radio receiving and transmittingapparatus, many of the parts of the apparatus such as coils, tubes andcondensers are equipped with electricall conducting shields which extendabout the parts and intercept and dissipate the fields of forcegenerated by or emitted from the part. The shields also serve tointercept fields of force generated outside of the same. Such shieldshave usually been made of solid metal of low electrical resistance suchas copper, brass or aluminum. This construction is heavy and expensive.A light sheet or film of the metal, on the other hand, is notself-sustaining and is readily bent or broken.

Iron and steel are ordinarily not used in such shields despite the factthat these metals are strong and relatively inexpensive. Iron, steel andother ferrous metals possess relatively high electrical resistance andhence are less efficient for intercepting and dissipating the fields offorce than copper and other metals of high conductivity and lowresistance. More important, how.- ever, is the fact that the ferrousmetals when used as shields tend to set up magnetic fields of force as aresult of the eddy currents which are created in the shield.Accordingly, instead of dissipating the fields of force, an iron orsteel shield will tend to set up fields of force of its own.

In accordance with the present invention, a shield is provided in whicha laminated tubular body contains a layer of ferrous metal and a layerof non-ferrous metal, the non-ferrous metal being adapted to interceptand dissipate the fields of force generated by or emitted by the currentsource, while the ferrous metal supports the body and further dissipatesany fields of force which may be brought into contact with the same. Inaddition, the non-ferrous metal serves to intercept and dissipate anfields of force which the ferrous metal itself may tend to set 119.

Another feature of the invention is to provide a light weight andinexpensive base for supporting the non-ferrous metal, the base being ofnon-conducting or insulating material. Another feature ls to provide alaminated tubular body in which a layer of ferrous metal and a layer of.non-ferrous metal are secured to each other in electrically conductingrelation.

A further feature of the invention is to provide a laminated tubularshield wherein a thin sheet of non-ferrous metal is spirally wound abouta non-conducting base with the edges of the sheet being in overlappingrelation to form a seam oblique to the axis of the base. The seam doesnot extend more than one revolution about the base. In this way, theadvantages of applying a sheet to a base by spirally windin areobtainedwhile at the same time the sheet does not extend about the base in a.plurality of revolutions which would tend to act as a coil and set up aninductance when subjected to electro-magnetic or electro-static fieldsof force. The invention is illustrated in the accompanying drawing inwhich- Figure 1 is a perspective view of a tubular shield constructed inaccordance with the invention; Fig. 2 is a longitudinal sectional viewtaken along the line 2-2 of Fi 1; Fig. 3 is a perspective view of amodification of the shield.

Referring particularly to Figs. 1 and 2, a laminated tubular shield I0is equipped with an outer casing II of iron or steel or other ferrousmetal. The casing II may be of any suitable size and shape and ispreferably of a thickness sufficient to make the casing self-sustainingwithout caus ing it to be excessively heavy. If desired, the casing, asshown, may be coextensive in length with the shield Ill.

Within the casing II is a thin layer I2 of copper foil or othernon-ferrous metal of relatively low electrical resistance. Within thelayer of copper foil I2 is a paper or other non-conducting base l3 whichin turn supports another layer I4 of copper foil. The paper base may, asshown, be composed of a plurality of layers or sheets of paper I5, I6and I! spirally wound together to form an integral tubular paper base.The layers I2 and I4 of copper or other foil may be secured to the paperbase in any suitable manner, preferably by an adhesive.

The copper sheet of foil I4 is spirally Wound about the inside surfaceof the paper base I3 with the edges of the sheet overlapping to form aseam I8 oblique to the axis of the tubular base. The seam l8 extendsabout the tubular base less than a single revolution. Similarly, thesheet of copper foil I2 is wound about the outside of the paper base andforms a seam which does not extend completely about the base.

The spiral winding of thin sheets of copper or other non-ferrous metalabout a tubular base to form a laminated structure, is described and setforth in detail in my copending application, Serial No. 397,197, filedJune 9, 1941, for Shield for high frequency electrical currents and mycopending application Serial No. 397,198, filed June 9, 1941, forLaminated tubular bodies and method of forming the same, which hasmatured to Patent No. 2,354,556, dated July 25, 1944. Accordingly, themethod of preparing such spirally woundtubular bodies will not bedescribed in detail herein.

Adjacent one end of the tubular shield Ill are a pair of spade bolts [9and which are equipped with flattened surfaces 2| and 22 respectivelyextending along the outside of the casing II on opposite sides thereof.Rivets 23 and 24 or other suitable means extend through the plates 2|and 22 respectively and also through casing H and the layers l2, l3 andM, the rivets serving to secure the spade bolts l9 and 20 to the shieldand also to bring the casing H into electrically conducting relationwith the sheets l2 and M of non-ferrous metal. The other ends 25 and 26of the spade bolts l9 and 20 respectively are threaded to provide studsfor the mounting of the shield.

The shield assembly thus includes, as shown, a substantially cylindricaltubular base ii of paper or other non-conducting material. Thin sheetsl2 and M of copper or other non-ferrous metal extend about the outer andinner surfaces respectively of the tubular base, the sheets beingspirally wound about the base and having their edges in overlappingrelation to form seams oblique to the axis of the base. The casing ll ofthe ferrous metal extends about and encloses the base l3 and the sheetsl2 and [4. If desired, the casing ll may be closed at one end and, if soconstructed, may be equipped with a layer of non-ferrous metal on theinside of the closure portion.

In the modification of the invention shown in Fig. 3, the tubular shieldis of square cross section but is otherwise constructed in a manneranalogous to that shown in Figs. 1 and 2. The tubular base 32 ofrectangular cross-section may be equipped with layers of foil of anon-ferrous metal extending about the inner and outer surfaces of thebase just as the non-conducting base I3 of Fig. 2 is arranged. The innerlayer of foil 33 is spirally wound about the inside of the tubular paperbase 32 with the edges of the sheet of foil in overlapping relationforming a seam 34 oblique to the axis of the base 32. The seam 34 ispreferably on only one of the rectangular sides of the tubular base andextends in a single plane. The layer of foil extending about the outsideof the tubular base is similarly arranged. The iron or steel casing 35is of square cross-section and snugly receives the base. Spade bolts 36and 31 are attached to the casing 35 and the base 32.

The term tubular is used herein in its broad sense and is intended toinclude hollow sleeve-like bodies of circular, polygonal, rectangular orother cross-section construction.

The shield may be assembled in any suitable manner. Preferably the baseof paper or other non-conducting material is provided with the layers ofnon-ferrous metal foil to form the laminated structure described and setforth in my copending applications referred to heretofore. Thislaminated structure may then be inserted in the tubular casing offerrous metal.

One method of forming a. shield of the construction set forth herein isto provide a tubular base or body which is self-sustaining, but isnevertheless collapsible, and to wind a strip of metal foil about thebase, the foil being wound at an angle as in spiral winding. Upon thelayer of foil may be placed a layer of paper laminations. Preferably,the paper is in the form of gummed tape or the like and is spirallywound about the metal foil. If desired, the strips of gummed tape andmetal foil may be wound simultaneously about the tubular base. Informing the structure shown in Figs. 1 and 2, a. second layer of metalfoil is wound at an oblique angle about the laminated paper layer and,if desired, thi foil may be applied simultaneously with additionalstrips of gummed tape which are spirally wound to form a laminatedtubular body about the outer layer of metal foil. The adhesive on thegummed tape may secure the first layer of metal foil to the intermediatelayer of tape. Similarly, adhesive may be used to secure the outer layerof metal foil to the intermediate layer of tape.

The shield may be formed as a tubular body of circular cross section andmay be readily converted into a polygonal tubular body by passing theshield over a mandrel of appropriate polygonal cross section. The innertubular base may then be withdrawn from the body and the outer paperlayer may also be removed.

The product which is formed by these operations contains two layers ofmetal foil, each wound at an angle as in spiral winding, the lay- I ersbeing separated by a layer of laminated paper, and each of the layersbeing adhesively secured to each other to form a unitary body. Thisproduct may then be inserted in the iron or steel casing to form theshield shown in Figs 1 and 2.

In forming the shield shown in Fig. 3, the metal foil is wound on thetubular bMe, and laminations of paper are applied to the foil, afterwhich the tubular base is collapsed and the product consisting of atubular body of paper with a foil layer on the inner side thereof may beinserted in the casing to form the shield.

The product shown in Fig. 4 may be made by the method described inconnection with the construction of Figs. 1 and 2, the circular productbeing converted into one of rectangular cross section by passing-it overa suitable mandrel.

When the shield is to be used, it is placed about the current source insuch a manner that the copper foil intercepts and dissipates theelectro-magnetic and electro-static fields of force generated by thecurrent source. Thus when the shield is to be used with a coil, it ismerely placed over the coil, the fields of force emanating from the coilare intercepted by the layer or layers of copper or other non-ferrousmetal. Any fields of force which are not dissipated by these layers areintercepted by the iron or steel casing which also acts, although lessefliciently, to dissipate the fields of force. At the same time, thecopper layers effectively dissipate any magnetic fields of force whichmay be set up in the iron or steel casing. By reason of the spiralwinding of the sheets of copper with the seam extending less than onerevolution about the tubular base, a simple structure is provided whicheflectively avoids the setting up oi the inductance currents in theshield.

The spade bolts and Ill may be used to mount the shield in an assembly.The shield may be of any suitable size and shape and may readily beadapted for the various types of current source with which it is to beused.

While there have been shown and described certain embodiments of theinvention, it is to be understood that it is capable of manymodincations. Changes, therefore, in the construction and arrangement ofthe parts may be made without departing from the spirit and scope oi theinvention as disclosed in the appended claims.

I claim:

1. A self-sustaining shield for electrical currents, comprising a rigidtubular casing of ferrous metal, a pair of spaced tubular sheets ofnon-ferrous metal of low electrical resistance disposed within saidcasing, a carrier for said tubular sheets which is of nonconductingmaterial and to which each of said tubular sheets is adhesively secured,and means for electrically connecting said sheets of non-ferrous metalwith said tubular casing.

2. A self-sustaining shield for electrical currents, comprising a rigidtubular casing of ferrous metal, a pair of spaced tubular sheets 01non-ferrous metal of low electrical resistance disposed within saidcasing, and a carrier for said tubular sheets which is of non-conductingmaterial and to which each of said tubular sheets is adhesively secured.

3. A self-sustaining shield for electrical currents, comprisin a rigidtubular casing of ferrous metal, a tubular sheet of non-ferrous metal oflow electrical resistance disposed within said casing and adjacentthereto, a second tubular sheet of non-ferrous metal of low electricalresistance within said first-mentioned tubular sheet and spacedtherefrom, a supporting tubular sheet of insulating material disposedbetween said tubular sheets, and layers of adhesive securing saidtubular sheets of non-ferrous metal to said insulating sheet, saidinsulating sheet being of suflicient rigidity to maintain saidfirstmentioned sheet of non-ferrous metal snugly against said rigidcasing.

4. A shield as set forth in claim 3 in which said tubular sheets arespirally wound.

5. A self-sustaining shield for electrical currents, comprising a rigidtubular casing of ferrous metal, a tubular sheet of paper within saidcasing, a tubular sheet of copper adhesively secured to the outer sideof said paper sheet and supported in position adjacent said casing bysaid paper sheet, tubular copper sheet within said paper sheet andadhesively secured thereto, and means for connecting said casing andsaid copper sheets with ground potential.

WILLIAM F. STAHL.

